The thermal decomposition mechanism of CH3NO2 has been studied by ab initio and MNDO methods. The potential-energy curves obtained with both methods are qual. consistent with each other. The canonical delocalized MO's given using ab initio calculation for CH3NO2 in its ground electronic state and at each point along the decomposition pathway are localized. The bonding localized sC-N-MO energy drastically increases and the sC-N-MO moves correspondently from the 5th to 16th-MO when the C-N distance changes from 1.6 to 1.8 ? According to the energy level and the phase of the FMO, HOMO, and LUMO, the formation of C-O bond by rearranging to CH3ONO is less likely to be the first step in the decomposition of CH3NO2. It is more likely that CH3NO2 decompose into radicals (.CH3+.NO2) initially.

Key words: NITRO COMPOUNDS, METHANE P, REACTION MECHANISM, COMPUTER APPLICATIONS, QUANTUM CHEMISTRY, THERMOLYSIS, ELECTRONIC STRUCTURE, AB INITIO CALCULATION, MOLECULAR ORBITAL THEORY